The invention relates to an element for providing electrical connection between a printed circuit board bonding pad and a metallic housing part via a friction-grip metal component.
In practice, electrical connections between a printed circuit board bonding pad and a metallic housing part, in particular for connecting to ground via the housing, are in most cases made via the friction-grip metallic part, usually a screw or a rivet, by pressing the electrical printed circuit board bonding pad against or onto the metallic housing part. However, since the printed circuit boards are of plastic material, they become deformed under the action of compression force in the aging process, which means that the quality of the electrical connection cannot be guaranteed over the life of the product. For this reason a separate grounding connection has been hitherto provided via a pin in the connector to guarantee secure ground bonding over the life of the product. Outside the subassembly the ground line is then bonded by tapping from the connector directly to the grounding metallic housing part by means of a cable lug which, however, is a very complex operation, as an additional pin in the connector, a tapping element, an external ground line and a cable lug are required and have to be fitted.
In a further solution the printed circuit board exhibits metallizations on both sides in the area of the printed circuit board bonding pad that are interconnected through the board by means of a feedthrough, as can be seen from U.S. Pat. No. 4,927,367, for example. Here, too, a deformation of the printed circuit board over the life of the product cannot be ruled out. Other grounding connections are described in DE 296 03 747 U1 and, in the form of elastic springs not having a mechanical load-bearing function, in U.S. Pat. No. 5,138,529 and U.S. Pat. No. 3,066,367.
Particularly worthy of note is JP 08069826, which describes a connecting element having a contact finger that is fixed in a hole in the printed circuit board by soldering. A base surface that initially projects from the board having a protrusion shaped like a bushing for feeding through the friction-grip part is bent over after soldering onto the printed circuit board. Although the base surface has large-area contact with the head of the friction-grip part, only the bushing-shaped protrusion projects through the printed circuit board and thus rests on its edge on the housing part. The aim of the initially projecting base surface is to avoid the traces of solder that otherwise collect at the edge of the bushing-shaped protrusion when flow soldering. The operation to mount on a housing part a printed circuit board having such a connecting element is complex, as the initially projecting connecting element first has to be secured with the contact finger on the printed circuit board, subsequently bent over into the printed circuit board and then finally fixed with the friction-grip part. In the process it has to be positioned precisely to ensure that the bushing-shaped protrusion is located exactly above the hole in the printed circuit board. To compensate for tolerances in the spacing between contact finger and bushing-shaped protrusion, the hole in the printed circuit board must be larger. The lateral work capacity of the projection is poor and would have to be compensated for by the housing. The area in which the bushing-shaped protrusion contacts with the housing part is restricted to the edge and therefore unfavorable under mechanical load. Some of the forces will be redistributed onto the printed circuit board situated between the base surface and the housing part.